Development and validation of analytical methodology by GC-FID using hexadecyl propanoate as an internal standard to determine the bovine tallow methyl esters content.

EN 14103:2003 and EN 14103:2011 were developed in order to determine fatty acid methyl ester (FAME) content of biodiesel. The internal standards (IS) of biodiesel include methyl heptadecanoate (MHD) and methyl nonadecanoate (MND), respectively. However, since these ISs are also present in bovine tallow methyl esters (BTME) or overlapping peaks, they have not been efficient. This work proposes an improved BTME determination method by using hexadecyl propanoate (HDP) as an IS. For this purpose, an analytical methodology by Gas Chromatography-Flame Ionization Detector (GC-FID) was developed and validated, where HDP demonstrated selectivity in retention time between peaks C16:1 and C18:0 for coconut and soybeans methyl esters and BTME, as well as resolution >1.5 for the BTME in split mode 30:1. Trueness in the determination of BTME content using the HDP as an IS was statistically equivalent to confidence interval of 95% for the null hypothesis statistic test, even when only 20% of the HDP was utilized in comparison with the IS concentrations defined by EN 14103:2003 and EN 14103:2011. This allowed the biodiesel analysis to be performed five times more with 1 g of HDP. Furthermore, the method developed enabled us to reduce the analysis time by 21.6%, without prejudice to the integration of peaks (C6:0 to C24:1). Regarding the repeatability and intermediate precision tests, results of RSD (%) ≤ 2% were reached. Additionally, the method developed has proved to be robust. HDP is a long-chain fatty alcohol ester absent from feedstocks used in biodiesel synthesis. It presents all of the characteristics for a good IS, ideal for application via internal standardization method, as recommended by EN 14103.

Standard Reference Material (SRM) 2378 fatty acids in frozen human serum. Certification of a clinical SRM based on endogenous supplementation of polyunsaturated fatty acids.

Dietary fatty acids can be both beneficial and detrimental to human health depending on the degree and type of saturation. Healthcare providers and research scientists monitor the fatty acid content of human plasma and serum as an indicator of health status and diet. In addition, both the Centers for Disease Control & Prevention (CDC) and the National Institutes of Health - Office of Dietary Supplements are interested in circulating fatty acids (FAs) because they may be predictive of coronary heart disease. The National Institute of Standards and Technology (NIST) provides a wide variety of reference materials (RMs) and Standard Reference Materials® (SRM®s) including blood, serum, plasma, and urine with values assigned for analytes of clinical interest. NIST SRM 2378 Fatty Acids in Frozen Human Serum was introduced in 2015 to help validate methods used for the analysis of FAs in serum, and consists of three different pools of serum acquired from (1) healthy donors who had taken fish oil dietary supplements (at least 1000 mg per day) for at least one month (level 1 material), (2) healthy donors who had taken flaxseed oil dietary supplements (at least 1000 mg per day) for at least one month (level 2 material), and (3) healthy donors eating "normal" diets who had not taken dietary supplements containing fish or plant oils (level 3 material). The use of dietary supplements by donors provided SRMs with natural endogenous ranges of FAs at concentrations observed in human populations. Results from analyses using two methods at NIST, including one involving a novel microwave-assisted acid hydrolysis procedure, and one at the CDC are presented here. These results and their respective uncertainties were combined to yield certified values with expanded uncertainties for 12 FAs and reference values with expanded uncertainties for an additional 18 FAs.

A novel method for measuring trace amounts of total sulphur-containing compounds in hydrogen.

A novel method for the analysis of total sulphur-containing impurities in a hydrogen matrix has been developed. This method has a limit of detection (LoD) significantly lower than that maximum amount fraction for sulphur-containing compounds (4 nmol mol(-1)) specified by the international standard for hydrogen to be used in fuel cell vehicles (ISO 14687-2). To measure the LoD for this method, a novel gas standard containing five different sulphur-containing compounds at low nmol mol(-1) amount fractions has been gravimetrically prepared. Stable primary gas standards that are traceable to the SI were used to successfully validate the amount fractions of the sulphur-containing compounds in this gas standards using gas chromatography with flame ionisation detection (GC-FID) and sulphur chemiluminescence detection (GC-SCD).

Liquid chromatography-flame ionisation detection using a nebuliser/spray chamber interface. Part 2. Comparison of functional group responses.

The application of a LC-nebuliser/spray chamber interface-flame ionisation detection has been demonstrated for the superheated water liquid chromatography of a wide range of aliphatic and aromatic analytes. The linearity and sensitivity of the response of volatile and involatile analytes have been compared. The response of the detector toward different analytes is similar to that in GC-FID and for volatile analytes was comparable to UV detection. However, the responses from involatile analytes, such as amino acids and carbohydrates, were poor and often lower than for a refractive index detector.

Comparison of a gas chromatography-optical fibre (GC-OF) detector with a gas chromatography-flame ionization detector (GC-FID) for determination of alcoholic compounds in industrial atmospheres.

An analytical methodology based on an optical fibre detector coupled to gas chromatograph has been developed for the speciation of some volatile alcoholic compounds. This methodology combines the separation capability of gas chromatography with an optical fibre detector made of an optical fibre sensitized with a thin polymeric film of poly[methyl(3,3,3-trifluoropropyl)siloxane] (PMTFPS). The response of the detector has been characterized at 650 nm for nine different alcohols (allyl alcohol, n-propyl alcohol, sec-butyl alcohol, isobutyl alcohol, n-butyl alcohol, isoamyl alcohol, methyl isobutyl carbinol, cyclohexanol and diacetone alcohol). An alternative method based on gas chromatography-flame ionization detector (GC-FID) was also used in order to evaluated the performance and compare the analytical results with the proposed method. The time of analysis, the analytical error and the analytical performance were similar for both methods. However, the analytical apparatus based on the GC-OF detector is much less expensive than the GC-FID and show high accuracy and suitability for actual monitoring on indoor atmospheres.

Determination of organotins in aquatic food by gas chromatography with pulsed flame photometric detection.

A method based on gas chromatography (GC)-pulsed flame photometric detection (PFPD) was developed to determine the levels of organotins in aquatic food. After being purified by gel-permeation chromatography in ethyl actate-tetrahydrofuran, the organotin compounds were derivatized by pentylmagnesium bromide. The derivative products were injected into the GC system and detected by PFPD (sulfur mode). The method was validated by analysis of the certified reference material and spiked samples. Recoveries of organotins ranged from 84.1 to 116.6% with relative standard deviation between 1.3 and 16.0% when spiked at levels of 2, 10, and 40 microg/kg. The limits of detection varied from 0.1 to 1.2 microg/kg for shellfish and 0.1 to 0.5 microg/kg for fish. The proposed method was suitable for determining organotins in aquatic foods.

Measurement of residual solvents in a drug substance by a purge-and-trap method.

The purge-and-trap (P&T) gas extraction method combined with gas chromatography was studied for its suitability for quantitative residual solvents determination in a water-soluble active pharmaceutical ingredient (API). Some analytical method performance characteristics were investigated, namely, the repeatability, the accuracy and the detection limit of determination. The results show that the P&T technique is--as expected--more sensitive than the static headspace, thus it can be used for the determination of residual solvents pertaining to the ICH Class 1 group. It was found that it could be an alternative sample preparation method besides the static headspace (HS) method.

Simple GC-FID method development and validation for determination of alpha-tocopherol (vitamin E) in human plasma.

This paper describes the development and validation of a novel GC-FID method for the determination of alpha-tocopherol concentration in human plasma which does not requires derivatization. The standard solutions and the plasma working solutions were prepared in absolute ethanol. To determine the concentration of alpha-tocopherol in human plasma, an aliquot of the plasma sample was deproteinized with ethanol. alpha-tocopherol was extracted with a mixture of hexane and dichloromethane (9:1). GC separation was performed using a HP-5 capillary column. Nitrogen was used as carrier gas at a flow-rate of 2 ml min(-1). Calibration curves were linear over the concentration range 1-30 microg ml(-1) (for standard solutions and solutions without endogenous alpha-tocopherol in plasma) and 5-34 microg ml(-1) (for solutions with endogenous alpha-tocopherol in plasma). Absolute recovery, precision, sensitivity and accuracy assays were carried out. The analytical recovery of alpha-tocopherol from plasma averaged 97.44%. The limit of quantification (LOQ) and the limit of detection (LOD) of method for standard samples were 0.35 microg.ml(-1) and 0.30 microg.ml(-1), respectively. Within-day and between-day precision, expressed as the relative standard deviation (RSD) were less than 4%, and accuracy (relative error) was better than 8%. This novel method, developed and validated in our laboratory, could be successfully applied to the in-vivo determination of alpha-tocopherol. The endogenous alpha-tocopherol amounts in blood of twelve healthy volunteers with no vitamin drug usage were measured with this method.

Determination of volatile residual solvents in pharmaceutical products by headspace liquid-phase microextraction gas chromatography-flame ionization detector.

This paper demonstrates headspace liquid-phase microextraction (HS-LPME) as used for the determination of volatile residual solvents in pharmaceutical products. This method is based on headspace liquid-phase microextraction capillary column gas chromatography. Under optimum conditions, the linerary of the method ranged from 1 to 1,000 mg l(-1). The limits of detection are 0.2-6.0 [corrected] mg l(-1) and relative standard deviations (RSD) for most of the volatile solvents were below 10%. This novel method is applied to the analysis of volatile residual solvents in pharmaceutical products with satisfactory results.

A contribution to the improvement of accuracy in the quantitation of THC.

The accuracy of a quantitative analysis is highly dependent on the quality of the reference standard. Although reference standards are more and more supplied with a certificate, laboratories may feel the need for additional acceptance testing. In general, confirmation of the purity of many solid reference substances can be obtained by a number of simple tests. However, verification of the true content of reference solutions may be complicated. A number of problems with the THC quantitation caused our interest for a verification method for the THC reference solution. The quantitation of THC is performed by gas chromatography with flame ionisation detector. The effective carbon number concept was used to predict GC/FID response factors. Equations and data are presented to calculate theoretical response ratios of cannabinoids. The experimental data for CBD and CBN were in excellent agreement with the theoretical ones. The paper shows that the response factors of CBD and/or CBN can be used for the calculation of the THC content of either reference solutions or cannabis samples.